US President Donald Trump has brought up the idea of investigating whom he considers the main obstacle on the path to reelection, former Vice President Joe Biden.

Trump told Politico in an interview Friday that it would be “appropriate” for him to discuss an investigation into Biden and his family ties in Ukraine with Attorney General William Barr.

“Certainly it is a very big issue and we’ll see what happens. I have not spoken to him about it. Would I speak to him about it? I haven’t thought of that. I mean, you’re asking me a question I just haven’t thought of,” said the president.

The investigation would be about Biden and his family’s business dealings in Ukraine as the vice president.

“Because he’s a Democrat it’s about 1/100 the size of the fact that if he were a Republican, it would be a lot bigger,” Trump said, adding that it could be “a very big situation” for Biden.

The 2020 Democratic contender reportedly threatened to withhold $1 billion in US loan guarantees unless Ukraine removed a top prosecutor looking into an energy company Biden’s son Hunter was a board member of.

After the allegations were released in a New York Times report, Trump’s personal attorney Rudy Giuliani called for an investigation into the matter.

During a Friday night appearance on Fox News, Giuliani said he had changed his mind about going to Ukraine and pushing for an investigation there.

“I’m not going to go,” Giuliani said. “I think I’m walking into a group of people that are enemies of the president, in some cases enemies of the United States, and in one case an already convicted person who has been found to be involved in assisting the Democrats with the 2016 election.”

The leading Democratic Party presidential candidate has previously called for impeachment of the Republican president over obstruction of justice amid the so-called Russia probe.

Trump suggested that Biden is his strongest rival among Democrats, asserting that “It seems that many of them aren’t registering with, you know, the public.”